The present invention relates to a new sodium perborate tetrahydrate of overall formula NaBO.sub.3.4H.sub.2 O or NaBO.sub.2.H.sub.2 O.sub.2.3H.sub.2 O, of special configuration, to a process for its manufacture, to its application for manufacturing a sodium perborate monohydrate of overall formula NaBO.sub.3.H.sub.2 O whose properties are particularly advantageous, and to the said perborate monohydrate.
It is known to manufacture sodium perborate tetrahydrate by processes based on the generation and agglomeration of particles of the said perborate from a supersaturated aqueous solution of sodium perborate.
In such processes, sodium perborate tetrahydrate of satisfactory quality, in particular exhibiting a good mechanical strength and a sufficiently low fines content can be obtained according to the state of the art only if the formation of excessively small particles is prevented, so that the agglomerates can form only from particles of sufficiently large sizes.
This principle, stated, for example, in French Patent No. 1,187,352, has not been questioned in the course of time, whether it has since been proposed to manufacture hollow agglomerates and not compact agglomerates, such as those described, for example, in French Patent No. 1,436,629, or to involve adjuvants such as anionic surface-active agents like those described, for example, in French Patents Nos. 2,1212,428, 2,228,718 and 2,455,564.
Thus, sodium perborate tetrahydrate known at present is in the form of agglomerated unit particles which are larger than approximately 40-55 m in size, and in most cases, furthermore, much larger than 50 m.